1. Field of the Invention
The present invention relates to an optimized method of transmitting news with multimedia content between a multimedia content transmitter and a multimedia content receiver in a mobile radio network.
2. Description of the Prior Art
The above kind of receiver can be connected to a radio broadcast network broadcasting collective news. This system is based on a network of terrestrial transmitters or geosynchronous or non-geosynchronous broadcast satellites, or a combination of broadcast satellites and terrestrial repeaters.
In the present description, the term “collective news” refers to news of interest to some or all users of a mobile radio system.
There are various prior art standards covering mobile telephone systems and architectures. They include the Global System for Mobile communications (GSM) and the more recent third generation (3G) standard for mobile transmission at high bit rates, known in Europe as the Universal Mobile Telecommunication System (UMTS). The term “GSM network” includes prior art services and enhancements known as GPRS and GERAN.
In the order in which they are cited above, these standards provide the benefit of increasingly high voice/data transmission bit rates for point-to-point connections (i.e. for a call between two users).
However, until now, few solutions have been offered for broadcasting collective news with multimedia content, for which the above standards are not suitable.
The term “broadcast” is used in the case of undifferentiated broadcasting to the whole of a population of users of a cellular mobile radio network, and the term “multicast” is used when news is addressed to a subset of that population. In the latter case, the subset of the population can be defined by a corresponding subscription, for example.
The Satellite Digital Multimedia Broadcast (SDMB) system for broadcasting to 3G mobile terminals can deliver multimedia content to 3G mobile terminals.
It is based on a geosynchronous satellite broadcasting to Europe a signal compatible with the standardized W-CDMA waveform used in UMTS terrestrial cellular networks. It operates in the IMT2000 satellite bands adjoining the IMT2000 terrestrial bands. To provide coverage in urban and suburban areas, the SDMB system also provides for the deployment of terrestrial repeaters. In the SDMB system, terminals are designed to operate in terrestrial cellular networks and to receive the SDMB satellite signal.
In the present context, the SDMB system cooperates with cellular networks to offer a low-cost multimedia content delivery and routing service with European coverage.
The transport layer of the SDMB system implements:                protection mechanisms to prevent loss of content based on the use of short-term and long-term forward error correction (FEC) techniques known in the art, or even carousel type retransmission, to alleviate transmission errors caused mainly by blocking of the satellite service link when the terminal is masked by an obstacle such as a building, a tree, a tunnel, etc., and        reactive protection mechanisms that take account of transmission errors a posteriori; these mechanisms include mechanisms for adjusting the FEC depth and, in the last resort, submitting requests for recovery of content blocks lost during transmission.        
The transport layer of the SDMB system uses a combination of the mechanisms previously cited with a bandwidth consumption in the satellite segment and by access to the return channels in the cellular networks that is a function of the required routing guarantee.
In the case of a high routing guarantee and a restricted deployment of terrestrial repeaters, the return channel of a terminal may be heavily accessed by the cellular network. This penalizes one objective of the system, namely reducing transmission cost.
To remedy this problem, it is possible to modify the preventive transport mechanisms by increasing the FEC depth. However, this solution increases the bandwidth consumed to transmit a content.
Another solution is to require lost blocks to be retransmitted only when the user wishes to access the content. However, this loses the benefit of content delivery aimed at statistically reducing the time to access the content.
The present invention aims to solve the above problems.